The invention relates to an improved fuel for use in pyrotechnic mixes which provides improved ignition rates and increased burning time without reduction in luminous intensity.
Pyrotechnic compositions produce light, heat, smoke or sound from an exothermic chemical reaction between a fuel and an oxidizer. Additives or modifiers have also been included to produce more saturated colored flames, to adjust burning rates, to produce colored smoke clouds, and to increase storage life and processing safety.
Pyrotechnic devices, which are employed in numerous munitions, have most commonly used magnesium and aluminum fuels since they are inexpensive, readily available and produce a large quantity of heat when they react with an oxidizer to form magnesium oxide and aluminum oxide, respectively. Pyrotechnic mixes with magnesium or aluminum, however, are difficult to ignite due to the high thermal conductivity of the metal, which tends to spread the energy from the ignition source away from the surface of the pyrotechnic and into the interior of the mix.
Once ignited, mixes with high percentages of metal burn faster than desirable, particularly with tracers and flares which are designed to be fuel-rich since their luminous intensity is augmented when aluminum or magnesium is vaporized and burned in air. Thus, the best flare is one with the maximum metal that can be vaporized, but as luminous intensity increases to a maximum, there is a corresponding increase in buring rate, which impairs efficiency. A conventional burning magnesium-sodium nitrate flare mix achieves maximum luminous intensity at approximately 72 percent by weight magnesium, as shown in the table below, but the rate of burning also increases to a maximum.
TABLE ______________________________________ Luminous Intensity and Burning Rate for a Series of Binary Magnesium-Sodium Nitrate Mixtures Mg Content, percent by Luminous Intensity, Burning Rate weight candles/cm.sup.2, .times. 10.sup.-3 cm/s ______________________________________ 20 0.70 6.1 30 6.0 19.6 42 15.8 33.3 46 24.0 39.6 50 27.9 41.9 60 59.8 67.8 70 106.2 99.1 75 121.7 109.2 80 88.4 109.2 85 69.0 81.3 ______________________________________
Applicant's novel pyrotechnic composition has succeeded in providing a metal which makes the pyrotechnic easier to ignite and which burns slower so that a high luminous intensity can be maintained over a longer period of time than that achieved in conventional metal fuel pyrotechnics.